rochleder's  proximate  analysis. 
275 
when  it  takes  place,  whether  a  more  or  less  elevation  of  temperature  re- 
sults, caused  by  heat  becoming  free,  in  consequence  of  the  combination  of 
the  aldehyde  or  aldehydes  with  the  bisulphite  of  potash.  When  no  reac- 
tion is  produced  at  ordinary  temperatures,  this  may  be  promoted  by  heat. 
Sometimes  after  the  solution  of  the  oil,  or  a  portion  of  it,  in  the  concen- 
trated aqueous  solution  of  the  bisulphite  of  potash,  by  long  standing  and 
cooling,  a  separation  of  crystals  results.  If  no  such  separation  is  observ- 
ed, the  undissolved  portion  of  the  oil  can  be  removed  mechanically,  and 
alcohol  carefully  added  to  the  solution,  by  which  the  separation  of  the 
aldehydes,  or  aldehyde  in  combination  with  the  bisulphite  of  potash,  is  fa- 
cilitated. Sometimes  the  addition  of  bisulphite  of  potash  quite  or  partly 
congeals  the  oil,  in  consequence  of  the  formation  of  a  compound  of  the 
aldehyde  with  bisulphite  of  potash.  In  this  case  the  solid  or  semi-solid 
mass  should  be  washed  with  alcohol,  and  the  washed  product  pressed  be- 
tween bibulous  paper.  If  neither  before  nor  after  the  addition  of  alcohol 
a  solid  compound  of  one  or  more  aldehydes  with  bisulphite  of  potash  re- 
sults, the  action  of  the  corresponding  soda-salt  is  tried,  and  when  this  af- 
fords no  solid  product,  the  corresponding  ammoniacal  bisulphite  should 
be  employed.  If  an  aldehyde,  or  several  of  them  together,  are  present, 
we  obtain  with  the  bisulphites  of  potash,  soda,  or  ammonia,  a  com- 
pound or  a  mixture  of  them,  from  which,  by  the  addition  of  dilute  sulphu- 
ric or  hydrochloric  aCid,  or  a  solution  of  caustic  potash  or  soda,  the  alde- 
hyde or  aldehydes  can  be  again  separated. 
In  the  same  way  here  described,  the  oil,  freed  from  acids  by  baryta 
water,  and  from  bases  by  dilute  sulphuric  acid,  is  treated  to  remove  the 
aldehyde  or  aldehydes  preseut.*  If,  after  the  separation  of  the  bases  and 
acids  or  aldehydes  present,  any  oil  remains,  this  portion  may  either  be  a 
hydrocarbon  or  a  mixture  of  several  such  bodies,  or  an  oxygenated  indif- 
ferent oil,  or  a  neutral  compound  ether,  or  a  mixture  of  several  of  these 
bodies. 
To  ascertain  whether  we  have  to  do  with  a  hydrocarbon  or  a  mixture  of 
several  hydrocarhoiis,  or  whether  an  oxygenaied  volatile  siibstanceis  also  pre- 
sent, a  fragment  of  sodium  or  potassium  is  introduced  into  the  oil,  previ- 
ously dried  by  means  of  chloride  of  calcium.  If  the  metallic  fragment 
remains  unacted  upon  in  the  fluid  even  after  the  application  ef  a  gentle 
heat,  no  oxygenated  body  exists  in  the  oil ;  consequently  the  oil  must  be 
^"  I  found,  by  the  examination  of  oil  of  origanum,  that  it  consisted  of  two 
volatile  oils,  which  aflforded,  when  heated  with  an  aqueous  solution  of  bisul- 
phite of  soda  or  ammonia,  a  solid  body,  but  which  contained  no  sulphur,  soda, 
or  ammonia.  I  have  deemed  it  necessary  to  call  attention  to  this  circumstance, 
as  it  is  highly  probable  that  there  are  many  other  volatile  oils  which  behave 
like  oil  of  origanum.  Consequently,  if  we  would  decide  with  certainty  on  the 
presence  of  an  aldehyde,  we  must  ascertain  whether  the  product  obtained  by  the 
action  all  alkaline  bisulphites  contains  sulphurous  acid,  or  the  alkali  employed 
in  its  preparation.  If  sulphurous  acid  and  a'  kali  cannot  be  detected,  no  aldehyde 
is  present. 
